Panels used in flat panel displays (hereinafter referred to as FPD's) are usually formed by cutting a mother substrate into a glass substrate of predetermined dimensions (unit substrate). Concretely, when a mother substrate is cut, scribe lines are created on the surface of a sheet of a mother substrate, and then, the above described substrate is broken along the created scribe lines.
Patent Document 1 discloses a technology for cutting a glass substrate using a cutter wheel.
FIG. 13 is a front diagram showing a well known scribing device used in the process for scribing a brittle material substrate.
The scribing method is described in reference to FIG. 13. Here, in the following description, the left-right direction is direction X and the direction perpendicular to the paper is direction Y in this figure.
As shown in FIG. 13, a scribing device 100 is provided with a table 150 which is horizontally rotatable and to which a mounted glass substrate G is secured using a vacuum suction means, a pair of guide rails 121 and 121 which are parallel to each other and support Table 150 so that Table 150 is moveable in direction Y, a ball screw 122 for moving Table 150 along guide rails 121 and 121, a guide bar 123 which is provided above Table 150 in direction X, a scribe head 130 which is provided on guide bar 123 so as to be slidable in direction X and applies a load to the edge of the below described cutter wheel 120, a motor 124 for sliding scribe head 130, a chip holder 140 which is provided at the lower end of scribe head 130 so as to be moveable upward and downward and which freely oscillates, a cutter wheel 120 which is attached to the lower end of chip holder 140 so as to be rotatable, and a pair of CCD cameras 125 which are provided above guide bar 123 and perceive alignment marks formed on glass substrate G placed on table 150.
FIG. 14 is a diagram showing an example of the process for cutting a mother substrate into unit substrates.
The method for cutting glass substrate G is described in reference to FIG. 14.
(1) First, as shown in FIG. 14(a), glass substrate G is mounted on the scribe table of the scribing device, and the upper surface (surface A) of the glass substrate is scribed using cutter wheel 120, so that a scribe line Sa is created. Vertical cracks created as scribe line Sa usually have a depth of 10% to 15% of the plate thickness of glass substrate G.
(2) Next, the above described glass substrate G is turned over and the above described glass substrate G is conveyed to a breaking device. Then, as shown in FIG. 14(b), a breaking bar 3 is pressed against the upper surface (surface B) of glass substrate G mounted on a mat 4 along the line facing scribe line Sa in this breaking device. As a result, the crack spreads upward from scribe line Sa on the surface A on the lower side of glass substrate G, and thus, glass substrate G is broken along scribe line Sa.
Each of the above described processes (1) and (2) is repeated once or a number of times depending on the type of glass substrate G, and therefore, glass substrate G is cut into unit substrates.
That is to say, in the case where glass substrate G is a single substrate, it is cut into unit substrates by carrying out each of the above described scribing and breaking once, while in the case where glass substrate G forms a liquid crystal display panel, the glass substrate to be cut is made up of glass substrates that are pasted together, and the processes (1) and (2) are carried out again after the above described breaking, and thus, the glass substrate is cut into unit substrates.
In the manufacture of a TFT liquid crystal display panel, for example, a TFT substrate and a color filter are pasted together and cut into unit substrates through scribing and breaking, each carried out two times, and after that, liquid crystal is injected into the gap between the TFT substrate and the color filter substrate which are pasted together, and thus, a liquid crystal display panel is gained. In recent years, mother substrates have increased in size, together with the increase in the size of display screens and rise in the demand for liquid crystal substrates. Accordingly, it has become difficult to turn over glass substrate G after scribing and convey glass substrate G to the breaking device as described above. Furthermore, mother substrates from the fifth generation onward (for example 1100 mm×1250 mm) have been cut into unit substrates through scribing and breaking, each carried out two times, after liquid crystal is injected through dripping. Therefore, when glass substrate G is turned over using, for example, a vacuum suction means, for breaking after liquid crystal has been injected through dripping, the space between the two substrates partially expands, causing a problem such that the gap between the substrates becomes uneven.
In the cutter wheel 10 for scribing a brittle material substrate of Patent Document 1, as shown in FIGS. 18 and 19, a V-shaped ridge line part 11 is formed as an edge along the circumferential part of a disk-like wheel, and furthermore, a number of protrusions 10a are formed in the above described ridge line part with a short pitch. When a scribe line is created using cutter wheel 10, cutting becomes possible without the breaking process being required, by applying scribing pressure for the formation of vertical cracks on the surface of the glass substrate with protrusions 10a, so that deep vertical cracks that reach no less than 80% of the substrate thickness extend in the vertical direction from the surface of the glass substrate.
Thus, cutter wheel 10 of Patent Document 2 has a high seepage force for glass substrates, making the glass substrate after scribing of an almost completely cut state, even without a breaking process being carried out, and therefore, the process for turning over a glass substrate in order to carry out a breaking process afterward can be omitted.    Patent Document 1: Japanese Unexamined Patent Publication S59 (1984)-8632    Patent Document 2: Japanese Patent No. 3,074,143